Short answer: surge protection with solar panels is not in every case rock-solid “legally required”, but the way the standard is written, in practice you almost never get out of it. The standard says: fit a surge protective device (an SPD), unless you can show with a risk assessment that it isn’t needed. If you don’t do that assessment, the SPD is required anyway.
And here’s the kicker for solar panels: the moment your installation needs an SPD on the grid side (the AC side), you also have to protect on the panel side (the DC side). That’s stated word for word in the standard.
For you as a homeowner with a PV system, in most cases that means: a Type 2 SPD belongs in your consumer unit, and often one at the inverter on the DC side as well. Reckon on roughly 150 to 400 euros installed by a qualified electrician, depending on whether it’s only the AC side or the DC side too.
Below I’ll explain exactly what one of these things does, why it counts double with solar panels, what the standard really says about it, and why this work on your consumer unit belongs with a professional and not with you on a Saturday afternoon.
What is surge protection, really?
Overvoltage is exactly what the word says: suddenly there’s far too much voltage on your wiring. Only very briefly, a fraction of a second, but with an enormous spike. Thousands of volts instead of your normal 230.
We call a spike like that a transient overvoltage. It can arise in two ways:
- From outside (atmospheric): a lightning strike nearby, not even on your own house. The strike induces a voltage spike in the grid and in your cabling.
- From within the grid (switching surge): the grid switching, a heavy machine at the neighbour’s kicking in or cutting out, or a fault in the network operator’s grid.
A surge protective device, in the trade an SPD (Surge Protective Device, also called a surge arrester), catches that spike. It sits quietly in your consumer unit and does absolutely nothing during normal operation. But the moment a spike comes past, it diverts it to earth at lightning speed. That keeps the voltage on your equipment within safe limits.
Think of it as an overflow in your sink. Normally you never notice it. But when it gets too full, the excess drains away neatly instead of spilling over your worktop.
What is a varistor and why does it wear out?
The heart of most Type 2 SPDs is a varistor. In full, a metal-oxide varistor, MOV for short.
A varistor is a voltage-dependent resistor. Sounds technical, is simple: at normal voltage it’s an insulator, it lets nothing through. But as soon as the voltage rises above a certain threshold, its resistance drops at lightning speed and it starts to conduct. At that moment it channels the surge current to earth. When the voltage drops again, the varistor closes back up.
Important to know: a varistor wears out. Every time it clears a hefty spike, a bit of its lifespan is spent. That’s why a good SPD has a status window: a small viewing panel that’s green while it still works and red or orange when the varistor is done. If that’s on red, you’re no longer protecting anything and the module has to be replaced.
That’s also the reason an SPD is not a “fit and forget”. During a periodic inspection of your installation, the professional should be checking that window.
Why does this matter extra with solar panels?
Three reasons a PV system is more vulnerable than an ordinary household.
One: you’ve got expensive electronics hanging up there. Your inverter is the brain of your system and the most expensive single component. A voltage spike is precisely what such electronics can’t handle. One hefty spike and your inverter is due for replacement, and that’s a stiff bill.
Two: there are long DC cables running across your roof. Those DC strings between your panels and the inverter act like a kind of aerial. If lightning strikes nearby, those long cable loops catch the induced spike and send it straight into your inverter.
Three: you’ve got kit at the highest point of your house. Panels on the roof sit literally closest to any possible strike. That raises the risk of your installation having to cope with a spike.
Note: it’s almost never about a direct hit on your house. That’s rare. The danger lies in nearby strikes and in switching spikes from the grid. Those happen far more often than you’d think, and that’s exactly what an SPD protects against.
Is surge protection required by the standard?
Here I need to be precise, because online people shout “yeah, required” far too easily. The truth is more nuanced, and that nuance is exactly what matters.
The Dutch NEN 1010 is the standard for low-voltage installations (in the UK the equivalent is BS 7671, the Wiring Regulations). The standard itself is not law, but it’s designated through the building regulations as the level you have to meet. For new installations and for changes and extensions to existing installations, the standard is therefore the level you must comply with. If you put solar panels on your roof, you’re changing your installation, and that changed part has to meet the applicable standard.
Now the core, section 443 of the standard. In short, it says:
- Surge protection is directly required if the consequences of an overvoltage affect, among other things, human life (think medical care), public services, or large groups of people.
- In all other cases (so an ordinary home) you must make a risk assessment under section 443.5 to determine whether it’s needed.
- And this is the provision it all hinges on: if you don’t do that risk assessment, the surge protection has to be applied anyway.
Translated to your situation: an SPD isn’t bluntly required in every home, but the standard forces you into a conscious choice. Either an electrician shows with a risk assessment that it isn’t needed, or the SPD goes in. In practice most electricians fit a Type 2 SPD as standard, because that’s safer, tidier and often cheaper than the extensive paperwork of a risk assessment.
For solar panels, section 712 comes on top of that. It states (section 712.443): if an SPD is needed on the AC side based on section 443, then that protection also has to be applied on the DC side. It’s that simple.
So the honest conclusion: “required with solar panels” cuts the corner too much, but “in most cases you can’t get around it” is absolutely true.
What’s the difference between a Type 1, Type 2 and Type 3 SPD?
There are three types and they don’t do the same thing. Don’t mix them up, because the wrong type gives false safety.
| Type | Protects against | Where it sits | Discharge current (In), rule of thumb |
|---|---|---|---|
| Type 1 | Direct lightning strike / with an external lightning protection system | At the supply point (service head) | At least 12.5 kA per connection (test class I) |
| Type 2 | Indirect lightning and switching surge | In the consumer unit, after the main switch | At least 5 kA (test class II) |
| Type 3 | Residual spikes, fine protection | Close to sensitive equipment | Supplementary, never on its own |
The broad strokes:
Type 1 you only need if your house has a genuine lightning protection system (those metal conductors down the roof, think churches and tall buildings). Then a direct strike can run down that conductor and you need Type 1 to handle that enormous current. Most ordinary homes don’t have such a system.
Type 2 is the workhorse for a normal home with solar panels. It catches the indirect spikes (a nearby strike) and the switching surges. This is what belongs in your consumer unit as standard.
Type 3 is fine protection, close to very sensitive equipment. A Type 3 must never work on its own. It always has to be combined with a Type 1 or Type 2 further up the installation.
Watch out for this misconception: many inverters have internal protection, but that doesn’t count as a full SPD under the standard unless the manufacturer explicitly confirms it’s suitable. So don’t rely on “it’s already in my inverter”. An inverter certainly never contains a Type 1.
Surge protection or lightning protection: are they the same?
No, and people confuse these constantly. They’re two different things.
Lightning protection (a lightning protection system, LPS) is the external system that catches a direct strike and safely conducts it to earth. That’s the air terminals, the down conductors along the facade and the earthing. The aim is to stop a direct strike setting your building on fire or breaking through to the inside. Most homes don’t have this and aren’t obliged to either.
Surge protection (the SPD) protects against the voltage spikes that travel through your cabling. So not the lightning itself, but the electrical aftershock that comes into your installation via the grid or via induction.
Put simply: lightning protection keeps the lightning outside the building, surge protection keeps the spike out of your appliances. For a normal home with solar panels it’s almost always about the second one: the SPD.
Where does the SPD go in the consumer unit, and how does AC and DC work?
The AC side (the grid side) is the best-known part. That’s where the Type 2 SPD belongs in your consumer unit, directly after the main switch. That way it protects everything sitting behind it.
Two things a professional has to get right there:
- Earthing. The SPD has to be able to shed its surge current. A good, low-impedance earth connection is the basis. Without a solid earth, an SPD is a dead lump of plastic.
- Back-up fuse. The SPD has to be connected with correct protection, with the right back-up fuse, so that at end of life it doesn’t take out the installation.
And then a detail that often goes wrong: the connecting leads of the SPD have to be short. The standard uses the well-known half-metre rule for this (section 534). The total length of the connecting conductors mustn’t be more than about 0.5 metres. Why so strict? Because every extra metre of conductor can generate hundreds to a thousand volts extra during a hefty spike. Leads too long and your protection only half works. This is exactly the kind of thing a layperson doesn’t know and a professional does.
The DC side (between the panels and the inverter) is the part that’s often forgotten in a normal home. As soon as you need an SPD on the AC side, section 712 requires protection on the DC side too. Especially if the DC cables on your roof are long, because then the chance of an induced spike is greater. That DC SPD sits at or near the inverter.
In short: only protecting the consumer unit and forgetting the DC side is half a job.
What does surge protection for solar panels cost?
Realistic ranges, no made-up daily prices.
| Item | Guide price |
|---|---|
| Type 2 SPD (material, AC) | 40 to 120 euros |
| Type 2 SPD installed (AC, in an existing unit) | 150 to 350 euros |
| DC-side SPD extra (material) | roughly 50 to 150 euros |
| Electrician’s labour | around 60 to 90 euros per hour, 1 to 3 hours of work |
The wide spread comes down to your situation. If there’s room in your consumer unit and it’s modern, it’s done in no time. If your unit is full or dated, an upgrade might come first.
Set that against what you’re protecting. Replacing an inverter quickly costs many times an SPD, and that’s before I count in your other equipment. For the money it takes to have decent protection in the unit, this is one of the cheapest insurances in your whole installation.
When you get a quote for solar panels, always ask explicitly whether surge protection is included, and whether that covers both the AC and the DC side. That saves you an unpleasant surprise later.
Can I fit an SPD myself?
No. And here I’m strict, just like with all work on the consumer unit.
You can buy an SPD module yourself, that’s fine. But fitting it into your consumer unit is work for a qualified electrician. Full stop.
Why so firm? A few reasons:
- You’re working on the installation behind the main switch, at 230 volts. Wiring it wrong can be life-threatening. People genuinely come to harm here.
- An SPD only works if the earthing is right, the back-up fuse is right and the connecting leads are shorter than that half metre. Do that wrong and you’ve got a module that protects nothing but appears to show green. False safety is worse than no protection.
- The moment someone works on your consumer unit, that changed part has to meet the applicable standard. A qualified electrician can certify that, you can’t.
- In the event of a claim (for instance after a lightning strike), your insurer wants to see it was professional work. DIY tinkering in the consumer unit is your weak spot then.
So: picking out and ordering the SPD yourself is perfectly fine, but leave the fitting into the unit to a professional. This is not a DIY job on the consumer unit.
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Frequently asked questions
Is surge protection legally required with solar panels?
Not rock-solid required in every case, but through the standard you usually can’t get around it. The standard demands an SPD unless a risk assessment shows it isn’t needed. If that assessment isn’t made, the SPD is required anyway. And if the AC side needs an SPD, the DC side has to be protected too.
Which SPD type do I need for my solar panels?
In an ordinary home without an external lightning protection system, a Type 2 SPD is the standard. It belongs in your consumer unit, and on the DC side at the inverter protection usually belongs too. You only need Type 1 with a genuine lightning protection system on the building.
Isn’t there already protection in my inverter?
Many inverters have internal protection, but under the standard it doesn’t count as a full SPD unless the manufacturer explicitly confirms it. An inverter certainly never contains a Type 1. So don’t rely on it blindly and have your electrician check what’s really in your installation.
How long does an SPD last?
As long as the varistor isn’t worn out. Every spike it clears costs a bit of lifespan. That’s why a good SPD has a status window: green means okay, red means replace. Have the window checked at a periodic inspection.
What does it cost to have surge protection fitted?
A Type 2 SPD installed on the AC side runs roughly between 150 and 350 euros. Add the DC side or an upgrade to your unit and it climbs. The material itself is often 40 to 120 euros; the rest is labour from a qualified electrician.
Does an SPD protect against a direct lightning strike on my house?
Not on its own. An SPD protects against voltage spikes that travel through your cabling, so against nearby strikes and switching surges. Against a direct hit you need a lightning protection system, which most homes don’t have and aren’t obliged to have.
Regards from Fred Schouten
PS: when your solar panels are being fitted, get your electrician to show you the status window of your SPD and note where it is. Most people don’t even know a few years on that they have one, let alone check whether it’s still green. An SPD on red protects exactly nothing. A quick look at that little window at the yearly check and you know your inverter really is still covered.